Natural convection heat transfer of supercritical binary fluid in a long closed vertical cylinder
Natural convection heat transfer of supercritical binary fluid in a long closed vertical cylinder
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超临界二元流体在长封闭立式圆筒内的自然对流传热
DOI：
10.1016/j.ijheatmasstransfer.2014.09.034
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发表时间：
2015
影响因子：
5.2
通讯作者：
Shen B.
中科院分区：
文献类型：
--
作者：
Long Z. Q.;Zhang P.;Shen B.
本文研究了超临界N2-Ar二元流体在高宽比为27的封闭垂直圆柱内的自然对流换热，瑞利数为9.0 × 1011 ~ 2.0 × 1014。圆筒的下部被加热，顶部被冷却。通过改变二元流体的组成和筒体冷端的平均温度，研究了自然对流的换热特性。随着Ra的增加，发现了三种不同的区域，即，层流热边界层区、过渡区和极限区，实验确定的两个临界瑞利数分别为Racrit 1 = 4.0 × 10 ~（13）和Racrit 2 = 1.14 × 10 ~（14）。层流TBL区和极限区自然对流的标度分别为Nu ‡ Ra0.22和Nu ‡ Ra 1/3。当自然对流经历近临界温度段时，流体热物性的剧烈变化导致Nu-Rac关系出现反常现象，即随着传热速率的增加，Nu-Rac关系出现拐点，临界温度越高，拐点对应的温度越高.流体中的二元组分对自然对流换热特性没有明显影响，只影响拐点处的温度，表现为伪纯流体（具有与二元流体相同热物理性质的假定纯流体）。
We study the natural convection heat transfer of supercritical N2–Ar binary fluid in a closed vertical cylinder with an aspect ratio of 27 in the Rayleigh number range of 9.0 × 1011–2.0 × 1014. The cylinder is heated at the lower part and cooled from the top surface. The composition of the binary fluid and the average temperature of the cold part of the cylinder are varied to investigate the heat transfer characteristics of natural convection. Three different regimes are found with the increase ofRa, i.e., Laminar thermal boundary layer (TBL) regime, Transition regime, and Ultimate regime, with the two critical Rayleigh numbers determined experimentally to beRacrit1≈ 4.0 × 1013andRacrit2≈ 1.14 × 1014, respectively. The scalings of natural convection in the Laminar TBL regime and Ultimate regime areNu∝Ra0.22andNu∝Ra1/3, respectively. When natural convection experiences near-critical temperature range, the drastic variations of the thermo-physical properties lead to an anomalous phenomenon where an inflection appears in theNu–Racorrelation with an increase in heat transfer rate, and the corresponding temperature of the inflection point becomes higher for the fluid with higher critical temperature. The binary components in the fluid show no apparent effect on the heat transfer characteristics of natural convection except affecting the corresponding temperature of the inflection point in the present study, and the binary fluid behaves as a pseudo-pure fluid (an assumed pure fluid with the same thermo–physical properties as the corresponding binary fluid).
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